Fog inhibitors for photographic emulsions



Patented May 8, 1951 FOG INHIBITORS FOR PHOTOGRAPHIC EMULSION S Robert E. Staufier and William F. Smith, Rochester, N. Y., assignors to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey No Drawing Application May 4, 1949, SerialNo. 91,427

8 Claims.

This invention relates to fog-inhibiting agents and stabilizers for photographic emulsions and to photographic emulsions containing them.

It is known that photographic emulsions, particularly ultra-sensitive emulsions or those containing optical sensitizers exhibit a tendency to form a deposit of silver in the emulsion. This deposit extends more or less uniformly over the entire emulsion and is known as fog. Photographic fog is of two types: local and eneral. Local fog is formed by exposure of the film or plate at undesired points as by a light leak in the camera. General fog is formed in a number of ways. It may be caused by the conditions under which the film or plate is stored such as conditions of high temperature or humidity or unusually long time of storage. The nature of the emulsion may also produce general fog as well as the conditions of development of the emulsion as by development for protracted periods of time or at temperatures above normal. We are primarily concerned with the fog and sensitivity changes in films or plates which have been stored under adverse conditions of temperature and humidity.

General fog and loss of sensitivity of the emulsion are especially likely to occur when the sensitive material is stored under conditions other than ideal, that is, under conditions of high temperature and humidity as in tropical regions.

It is an object of the invention to provide novel anti-fogging or fog-inhibitin compounds for emulsions. A further object is to provide antifogging agents which stabilize the initial sensitivity of the emulsion; A still further object is to provide anti-fogging agents which improve the keeping of the emulsion in tropical regions. Other objects will appear from the following description of our invention.

These objects are accomplished by incorporating into a silver halide emulsion an acido-tetrammine-platinum complex e. g., a tetrammineplatinous halide, carbonate, nitrate or sulfate, or a dialkyleneplatinous halide, carbonate, nitrate or sulfate. Typical compounds provided as examples of those useful in our invention are: tetrammineplatinous chloride and bromide Pt (NI-I3 4Cl2 and Pt(N'H3)4Brz, diethyleneplatinous chloride and .bromide Pt(C2H4)2C12 and Pt(CzH4)2Br2, and diethyleneplatinous nitrate, Pt (C2H4) 2 (N03) 2. These compounds may be called acido-platinum complexes in which the ammonia or ethylene groups exist in the cation strongly bonded'to the platinum atom and the anion of the complex is a mon-ovalent or divalent anion of an acid.

The object of our invention is to maintain the sensitivity and fog of silver halide emulsions at or close to initial optimum values under keeping conditions of high temperature and humidity. The fog inhibitors which we propose to use are added to the emulsion during the process of manufacture to avoid loss of sensitivity and to inhibit the growth of fog with passage of time under non-ideal conditions of storage.

A solution of the compounds of the invention when added in suitable concentration before coating to unsensitized or optically sensitized photographic emulsions does not appreciably affeet the sensit-ometric values for sensitivity and fog when measurements are made soon after coating. When sensitometric measurements are made at appreciable intervals of time under tropical or dry conditions of storage at elevated temperatures, however, this compound does stabilize photographic speed and maintain fog at a low level.

The preparation of silver halide emulsions involves three separate operations (1) the emulsification and digestion or ripening of the silver halide, (2) the freein of the emulsion from excess soluble salts usually by washing, (3) the second digestion or after-ripening to obtain increased sensitivity. (lvl'ees, The Theory of the Photographic Process, 1942.) We prefer to add the fog-inhibiting agents after the final digestion or after-ripening although they may be added before digestion. The most useful concentration range of fog inhibitor is from .26 to 3.9 gm. of fog inhibitor per kilogram of silver nitrate used in making the particular silver halide emulsion and converted to silver halide. The quantity used will of course vary for example depending on the silver halide or mixture of halides and the particular compound used.

The anti-foggant and stabilizin action was determined by incubation of the emulsions under simulated tropical conditions and also by incubation at low relative humidity at F. for various lengths of time from 12 days to one month. The results of these tests are tabulated here and are compared with the initial speed, gamma and fog of the emulsions with and without the anti-foggant and stabilizing compound. The tests from which the following tabulation was made used a high-speed silver bromoiodide emulsion exposed on an Eastman type IB sensitometer and developed for five minutes in a developer of and equivalents falling within the scope of the the following composition: appended claims.

Grams We claim: Monomethyl paraminophenol sulfate 2.5 l. A silver halide emulsion containing an acido- Sodium sulfite (desiccated) 30 5 platinum complex as a stabilizing agent said com- Hydroquinone 2.5 plex containin a platinum atom in the cation. Sodium metaborate 2. A silver halide emulsion containing an acido- Potassium bromide 0.5 tetrammineplatinous complex as a stabilizing Water to one liter. agent.

Original 4 Wk. Tropical Gms.o1' compound per i ass 11 ver e o g m N0 emulsion i g Gamma Fog ig Gamma Fog l Control none 1,180 1.24 .06 780 1.07 .22 2 do none 980 1. 29 07 460 1.3 V. 22 3.. Pt(NHa)4Cl2-- 1.5 1,380 1. 21 .13 200 1.2 .18 4 Control none 1,850 1.30 .21 1,120 .96 .35 5 -410 none 2, 200 1. 2s .22 1, 400 1. 0 .3 o P00350201... 0.5 1, 900 1. so .12 2,500 .85 .21

One of the advantages of our invention lies in the fact that the compounds are readily prepared with high purity. Compounds are prepared by the method described in Textbook of Inorganic Chemistry by M. M. J. Sutherland, published by Charles Grifiin and Company, Ltd, London, vol. 10, pages 193 to 243 (1928).

The fog inhibitin agents which we have de scribed may be usedin various kinds of photographic emulsions. In addition to being useful in ordinary non-sensitized emulsions they may also be used in orthochromatic, panchromatic and X-ray emulsions. If used with sensitizing dyes, they may be added to the emulsion before or after the dyes are added. Various silver salts may be used as the sensitive salt such as silver bromide, silver iodide. silver chloride and mixtures of these. The dispersing agents may be gelatin or other colloid such as collodion, albumen, cellulose organic derivatives or synthetic resins.

We also contemplate as a part of our invention those cases where it is desirable to coat the antifoggant in a colloid layer such as gelatin on either or both sides of or also in a silver halide emulsion layer, so that the antifoggant is contiguous to the silver halide emulsion. In these cases we use the same or a slightly greater ratio of rare metal salt to silver halide as when the salt is in the emulsion layer.

It will be understood that we contemplate as included within our invention all modifications 3. A silver halide emulsion containing a tetrammineplatinous halide as a stabilizing agent.

4. A silver halide emulsion containing tetram- 25 mineplatinous chloride as a stabilizing agent.

ROBERT E. STAUFFER. WILLIAM F. SMITH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,120,429 Willis 1 Dec. 8, 1914 1,120,580 Willis Dec. 8, 1914 2,448,060 Smith et a1 Aug. 31, 1948 2,448,857 Brice Sept. 7, 1948 

1. A SILVER HALIDE EMULSION CONTAINING AN ACIDOPLATINUM COMPLEX AS A STABILIZER AGENT SAID COMPLEX CONTAINING A PLATINUM ATOM IN THE CATION. 